Add TRASH_AUTO_DELETE_DAYS to .env.template

.env.template

@@ -201,6 +201,10 @@
 ## Limit in kilobytes for a users attachments, once the limit is exceeded it won't be possible to upload more
 # USER_ATTACHMENT_LIMIT=
 
+## Number of days to wait before auto-deleting a trashed item.
+## If unset (the default), trashed items are not auto-deleted.
+## This setting applies globally, so make sure to inform all users of any changes to this setting.
+# TRASH_AUTO_DELETE_DAYS=
 
 ## Controls the PBBKDF password iterations to apply on the server
 ## The change only applies when the password is changed